public class BinaryTree {

    static class TreeNode {
        public char val;
        public TreeNode left;//左孩子的引用
        public TreeNode right;//右孩子的引用

        public TreeNode(char val) {
            this.val = val;
        }
    }


    /**
     * 创建一棵二叉树 返回这棵树的根节点
     *
     * @return
     */
    public TreeNode createTree() {
        TreeNode node1=new TreeNode('A');
        TreeNode node2=new TreeNode('B');
        TreeNode node3=new TreeNode('C');
        TreeNode node4=new TreeNode('D');
        TreeNode node5=new TreeNode('E');
        TreeNode node6=new TreeNode('F');
        TreeNode node7=new TreeNode('G');
        TreeNode node8=new TreeNode('H');
        node1.left=node2;
        node1.right=node3;
        node2.left=node4;
        node2.right=node5;
        node5.right=node8;
        node3.left=node6;
        node3.right=node7;
        return node1;


    }

    // 前序遍历
    public void preOrder(TreeNode root) {
        if(root==null){
            return;
        }
        System.out.print(root.val+" ");
        preOrder(root.left);
        preOrder(root.right);
    }

    // 中序遍历
    void inOrder(TreeNode root) {
        if(root==null){
            return;
        }

        inOrder(root.left);
        System.out.print(root.val+" ");
        inOrder(root.right);
    }

    // 后序遍历
    void postOrder(TreeNode root) {
        if(root==null){
            return;
        }
        postOrder(root.left);
        postOrder(root.right);
        System.out.print(root.val+" ");

    }

    public static int nodeSize;

    /**
     * 获取树中节点的个数：遍历思路
     */
    void size(TreeNode root) {
        if(root==null){
            return;
        }
        nodeSize++;
        size(root.left);
        size(root.right);
    }

    /**
     * 获取节点的个数：子问题的思路
     *
     * @param root
     * @return
     */
    int size2(TreeNode root) {
        if(root==null){
            return 0;
        }
        return 1+size2(root.left)+size2(root.right);
    }



    // 获取叶子节点的个数：遍历思路

  public static int leafSize = 0;

    void getLeafNodeCount1(TreeNode root) {
        if(root==null){
            return;
        }
        if(root.left==null&&root.right==null){
            leafSize++;
        }
        getLeafNodeCount1(root.left);
        getLeafNodeCount1(root.right);
    }

 //    获取叶子节点的个数：子问题
    int getLeafNodeCount2(TreeNode root) {
        if(root==null){
            return 0;
        }
        if(root.left==null&&root.right==null){
            return 1;
        }
        return getLeafNodeCount2(root.left)+getLeafNodeCount2((root.right));
    }


    //获取第K层节点的个数

    int getKLevelNodeCount(TreeNode root, int k) {
        if (root==null){
            return 0;
        }
        if(k==1){
            return 1;
        }
        return  getKLevelNodeCount(root.left,k-1)+getKLevelNodeCount(root.right,k-1);
    }


     //获取二叉树的高度
    // 时间复杂度：O(N)

    int getHeight(TreeNode root) {
        if(root==null){
            return 0;
        }
        int heightLeft=getHeight(root.left);
        int heightRight=getHeight(root.right);
        return (heightLeft>heightRight ? heightLeft:heightRight)+1;
       
    }


    // 检测值为value的元素是否存在
    TreeNode find(TreeNode root, char val) {
        if(root==null){
            return null;
        }
        if(root.val==val){
            return root;
        }
        TreeNode findLeft=find(root.left,val);
        if(findLeft!=null){
            return findLeft;
        }
        TreeNode findRight=find(root.right,val);
            if(findRight!=null){
                return findRight;
            }

        return null;
    }

}